1. Field of the Invention
This invention relates to a vibration isolating device for damping vibrations from vibration source.
2. Description of the Prior Art
The vibration isolating device generally called as a rubber vibration isolator and is used, for example, as an engine mount for automobile vehicles, whereby vibrations from an internal-combustion engine are absorbed so as not to be transmitted to a vehicle chassis.
As the vibration isolating device of this type, there has been proposed a vibration isolating device comprising two vibration-damping liquid chambers separated by a partition member provided with a restricted passage, in which vibrations from vibration source are absorbed by a flow resistance subjected to the liquid when the vibration is transmitted to the one chamber to thereby flow the liquid from the one chamber to the other through the restricted passage. In this device, not only is the vibration transmitting force lowered as far as possible at various vibration frequencies, but also the damping force is developed at a frequency range of 10-20 Hz corresponding to the vibration from the engine.
In the conventional engine mount, however, it is very difficult to absorb vibrations of a particular frequency other than the engine vibration. That is, when the vibration input to the engine mount is a high frequency, the amplitude is small to clog the restricted passage, so that the pressure inside the liquid chamber rises to increase the dynamic spring constant. As a result, the vibration transmitting rate is undesirably raised to deteriorate the ride comfort on the vehicle.
As a countermeasure for solving the latter problem, there has also been proposed a vibration isolating device capable of absorbing high-frequency vibrations, but it is not yet sufficient to damp those high-frequency vibrations. Therefore, it is strongly demanded to develop a vibration isolating device capable of damping vibrations at a wider frequency range.